Commitments and Contingencies - Operating Leases (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Rent expense	$ 84	$ 266
Operating lease right of use asset obtained in exchange for lease liability		470
Operating lease payments for the remainder of 2019	67	67
2020	270	270
2021	246	246
2022	178	178
2023	166	166
Thereafter	582	582
Imputed interest	$ 217	$ 217
Weighted average discount rate	4.20%	4.20%
Operating lease weighted-average remaining lease term	7 years 3 months 18 days	7 years 3 months 18 days
Operating lease payments		$ 271
Other assets [Member]
Long-term Purchase Commitment [Line Items]
Operating lease right-of-use assets	$ 1,200	1,200
Accrued Liabilities [Member]
Long-term Purchase Commitment [Line Items]
Current operating lease liability	243	243
Other liabilities [Member]
Long-term Purchase Commitment [Line Items]
Noncurrent operating lease liability	$ 1,000	$ 1,000